What follows this header — a transport protocol, or an extension header.
The same registry of numbers as IPv4's Protocol field, doing the same job, with one addition: it can also name an extension header, which then carries its own Next Header. That is how IPv6 replaced IPv4's fixed options field with a chain.
| Value | Meaning |
|---|---|
| 6 | TCP |
| 17 | UDP |
| 58 | ICMPv6 |
| 44 | Fragment header |
Bit values written MSB first, matching network byte order.
IPv6 Packet > Next Header